Posts Tagged “homebrew”


We have a young child that tends to wake up several times in the middle of the night and wanders around. He is Mr. Houdini and can escape any child proof system.  We have found him outside in the middle of the night while it was raining, and he was happily playing with his trucks.  We needed some sort of system that would wake US up if he got out of bed.  This project is the result.

We have used the X10 system for several years to control lamps, Christmas lights, and decorative fountains.  The X10 system sends and receives signals that are put onto the power lines inside the walls of the house.  There are also wireless modules that will detect a radio signal, and upon detection, it will send the proper X10 ON or OFF signal through the house’s power lines.  I devised a combination of these devices to turn on a simple homebrew oscillator that we put in our bed room.  When our child gets up, it turns on the alarm in our room, and we can short circuit our child’s plans.  Over time, he is slowly learning that he can not be successful in getting up in the night, and will stay in bed and fall back to sleep.

This is the setup:  We put a wireless motion detector above our child’s head on the wall.  It will not detect anything during his normal tossing and turning but if he gets up, the detector will detect his motion and send a radio signal to a receiver.  The receiver is plugged into an outlet in the hall; and transfers the signal it received to the house wiring where it is sent to our bed room.

In our bedroom, we have a module plugged into an outlet, that is constantly monitoring the house wiring for signals.  When it receives the appropriate signal, it turns power on to the outlet on the bottom of the device.  I have an AC adapter plugged into the module that powers a small alarm that sits on my bed stand.

The alarm, is a simple NE556 dual timer circuit.  It is wired up in a fashion that emits a BEEEP BEEEP BEEEP, on and off at half second intervals.  The frequency of the BEEEP is about 700 Hz.  Not too high pitch, and not too low. The circuit is built inside an Altoid Mints tin.

When the alarm goes off, one of us will get up and put our child back to bed.  We then use the remote control to send a wireless signal to the radio receiver in the hall outlet.  The receiver then sends the signal over the power line again back to our bed room, and shuts off the alarm.

I built an LED into the Altoid’s tin as a visual indication when the alarm is on.  I also put a switch on the tin to shut off the speaker in the tin.  This is because we don’t want the alarm to be tripping all day long whenever someone is in the bedroom.  Also, the motion detector will send an “OFF” signal if there is no more motion in its range within a certain amount of time.

Click HERE to see a larger slide show of the setup.

73, John

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